In 1978, we studied 3 groups of steelworkers 45 to 55 yr of age who were all smokers: "obstructive" smokers (OS) with a FEV1/VC less than 66.6% (59.8% in average) (n = 37), smokers with "small airways disease" (SAD) and an abnormal closing capacity and/or slope of phase III (delta N2) but normal FEV1/VC (n = 32), and "resistant" smokers (RS) with normal functional indices (n = 36). Smokers with SAD had a lower (p less than 0.05) FEV1/VC (71.7%) than did RS (74.9%). We studied again 6 yr later about 85% of survivors in each group. Analysis of variance showed that FEV1 decreased significantly (p less than 0.001) only in OS (from 2.67 to 2.46 L). In RS and smokers with SAD, FEV1 declined from 3.34 to 3.26 L and from 2.95 to 2.85 L, respectively (p greater than 0.05). In all 3 groups, delta N2 increased (p less than 0.001) from 0.77 to 1.30% N2/L in RS, 1.41 to 2.43% N2/L in smokers with SAD, and 2.22 to 4.20% N2/L in OS. A multivariate analysis showed that the initial N2 explained about 30% (p less than 0.001) of the decline in FEV1 in OS, but only 10% (p less than 0.001) in the 3 groups together. In fact, the link between delta N2 and fall in FEV1 was restricted to OS. Closing volume and maximal expiratory flow rates were not related to decline in FEV1. The link between uneveness of ventilation and subsequent loss of FEV1 is of physiopathologic interest.(ABSTRACT TRUNCATED AT 250 WORDS)